dotnet/roslyn

Confusing error when assigning result of ref readonly-returning method to a ref local

Open

#28,653 建立於 2018年7月18日

在 GitHub 查看
 (0 留言) (0 反應) (0 負責人)C# (20,414 star) (4,257 fork)batch import
Area-CompilersBugConcept-Diagnostic Clarityhelp wanted

描述

Version Used: 2.8.2; master from 14 July 2018 (c4189de08b943f87d9f03d45ef01e615800e359d)

Steps to Reproduce:

Try to assign the result of a ref readonly-returning method to a non-readonly ref local:

class C
{
    void M()
    {
        ref int x = ref Bar();
    }
    
    ref readonly int Bar() => throw null;
}

Actual Behavior:

error CS8329: Cannot use method 'C.Bar()' as a ref or out value because it is a readonly variable

I think this is not a good error message because:

  1. It's not correct: method is not a variable.
  2. It does not explain well what the error is and how to fix it.

貢獻者指南

技術棧
csharp
領域
developer experiencetooling
議題類型
bug
難度面向新貢獻者的預計實作難度，1 表示很小改動，5 表示專家級工作。
3
預計時間有經驗貢獻者完成調查、實作、測試並準備 pull request 的粗略時間範圍。
half day
活動狀態議題目前的可參與程度：新鮮、活躍、陳舊、阻塞或等待維護者輸入。
stale
清晰度議題是否清楚說明預期改動、驗收標準和下一步。
clear
前置要求
C# ref readonly featureRoslyn error message infrastructure
新手友善度1-100 的估計分數，表示該議題對首次貢獻者的友善程度。
30
研究方向
The issue reports a confusing error message CS8329 when assigning a ref readonly method return to a ref local. The fix involves locating the error message in the Roslyn source code, likely in ErrorFacts.cs or related error reporting files, and rewording it to be more accurate. The new message should clarify that the issue is using a ref readonly method result as a ref or out value. Review existing tests for CS8329 to ensure they pass after the change. Consider whether a new error code is needed or if the existing one should be updated.